Cerebral vasospasm occurs in up to 50% of patients presenting with a subarachnoid hemorrhage (SAH), the most common cause of which is a ruptured intracranial aneurysm. This delayed process has traditionally been associated with a short-term but marked reduction in the lumen of a major cerebral artery, and thereby a reduction of distal blood flow that results in cerebral ischemia or infarction. Despite advances in neuroradiology and neurosurgery, cerebral vasospasm remains the leading cause of morbidity and mortality in patients with SAH. The primary reason for this current clinical situation is that we still do not understand well the basic mechanisms by which "vasospasm" occurs. Indeed, recent results from the CONSCIOUS-1 Clinical Trial suggest that delayed cerebral ischemia and infarction following SAH may involve many other factors in addition to the enigmatic changes in large artery caliber, structure, and function. These additional key factors may include acute brain injury, thromboembolism of small vessels, cortical spreading depression, and of particular note herein, microcirculatory dysfunction. Because of the historical focus on large vessel changes, however, little quantification is available on the relative contributions of these other factors. The goal of this R21 application, therefore, is to quantify, for the first time, biomechanical, functional, and immunohistochemical changes in cerebral arterioles that result from blood clot associated constrictors, smooth muscle mitogens, and transglutaminases that are presented to the adventitial surface (as in SAH), with particular attention to expected short-term (3-5 day) structural and functional remodeling. Toward this end, we will use our recently developed perfusion organ culture system for ~100 micron diameter arterioles to study both individually and in combination the effects of adventitially-presented endothelin-1 (ET-1, a potent vasoconstrictor and mild mitogen), platelet derived growth factor (PDGF-AB, a potent mitogen and mild vasoconstrictor), and plasma transglutaminase (pTG a potent matrix cross-linker). Of the many molecules released into the subarachnoid space due to a subarachnoid hemorrhage, these potent molecules were selected based on clinical findings in patients showing that they play key roles in vasospasm as well as recent studies on extracranial arterioles showing the ability of ET-1, PDGF, and pTG to induce marked inward remodeling within 4 days. Our study will be the first, however, on potential remodeling of cerebral arterioles and the first to test the hypothesis that diverse inhibitors have potential to block, or at least reduce, this inward remodeling by exploiting vasodilatory, anti-proliferative, and anti-crosslinking actions. Data will be collected from isolated New Zealand White Rabbit cerebral arterioles to enable comparison with the large data base on rabbit large artery remodeling due to vasospasm and will provide significantly increased data on microcirculatory dysfunction. PUBLIC HEALTH RELEVANCE Recent clinical findings and seemingly unrelated basic science findings on remodeling of arterioles collectively provide compelling motivation for a new hypothesis for the role of vascular remodeling in cerebral vasospasm, a significant cause of morbidity and mortality in patients following rupture of a cerebral aneurysm. This study will be the first to propose and test this new hypothesis as well as a potential means to block this remodeling.